The present invention relates to a process for the production of a vinyl graft polymer emulsion and a high molecular weight polymer emulsion having excellent coating film properties.
Synthetic resin emulsions have been widely used for paints, adhesives, fibers, papers or the like.
The paints produced from an aqueous emulsion of a synthetic resin are more advantageous than solvent type paints, because they do not have such defects as being susceptible to fire, poisoning, and air pollution which have occasionally occurred when using the solvent type paints. Besides, the paints produced from high molecular weight polymers have a lower viscosity than the solvent type paints, and hence, can be used in a high concentration, whereby they have an excellent workability for painting and easy management after painting. However, the paints have some defects, such as a lower water resistance due to the use of an emulsifier or a protective colloid, inferior glossiness of the coating film, and inferior air-tightness of the coating film. From these standpoints, there have been conducted various studies on curable or uncurable high molecular weight emulsifiers which can be used instead of water-soluble or hydrophilic, low molecular weight emulsifiers which cause the undesirable lowering of the performances of the paints, such as lowering of water resistance.
It is described in Japanese Patent Publication No. 43381/1974 and Japanese Patent Laid Open Publication (without examination) No. 73488/1973 that an emulsion is produced by polymerizing a vinyl monomer in the presence of maleinated polybutadiene or maleinated butadiene copolymer as an emulsifier. As a result of re-examination of this process, the present inventors have found that the emulsion produced by the process described in Japanese Patent Publication No. 43381/1974 has an inferior stability and further inferior properties of the resulting coating film such as inferior water resistance and corrosion resistance, because the maleinated product of polybutadiene having many 1,4-bonds in the molecule has the double bonds within the inner part thereof and hence the graft polymerization with the vinyl monomer hardly proceeds. For eliminating the defects of this process, the present inventors have tried to enhance the graft polymerization activity of the maleinated product of polybutadiene. As a result, it has been found that the object can be accomplished by adding a compound having a vinyl-polymerizable double bond to the maleinated product of a polydiolefin having many 1,4-bonds or a copolymer thereof.
The vinyl graft polymer emulsion of the present invention has various advantages. For instance, when it is compared with so-called non-graft emulsion which is produced by emulsion-polymerizing a vinyl monomer in the presence of a neutralized product of the liquid polybutadienemaleinated product having many 1,4-bonds as the emulsifier, the emulsion of the present invention has more fine particle size of emulsion and further an improved freeze stability, miscibility of pigment and mechanical stability, as shown in examples and reference examples hereinafter.
The superiorities of the present emulsion are further realized when the emulsion is formed into a dry coating film. That is, the drying of the coating film made from the present emulsion is far faster than that made from the non-graft emulsion. In the non-graft emulsion, a metallic drier should be added. If the metallic drier is not added, extended periods of time are required for the coating film to dry as tested by finger touch, and when the coating film is very thick, it is impossible to cure completely. In the graft emulsion of the present invention, the coating film can be cured within a short time at room temperature without adding the metallic drier. The cured coating film has excellent chemical resistance, water resistance and also excellent glossiness. When a metallic drier is added to the graft emulsion of the present invention wherein the base polymer still has a few unsaturated groups, there can also be obtained a coating film having a higher degree of hardness.
Thus, the coating film made from the graft emulsion of the present invention shows far greater drying characteristics and also far greater water resistance and chemical resistance in comparison with the coating film made from the non-graft emulsion.
These superior properties of the coating film of the present invention may be as a result of the improved homogeneity of the resin system wherein the base polymer is grafted, while the homogeneity in the non-graft system is substantially inferior.
The present inventors have found that the desired emulsion, which can give a coating film having excellent water resistance and glossiness, can be produced by emulsion-polymerizing a vinyl monomer using as the emulsifier a partially esterified, imidated or amidated product of an adduct of a diene polymer (e.g. polybutadiene, polyisoprene, or copolymer of butadiene or isoprene with another monomer), a natural drying oil or a natural semidrying oil with an .alpha.,.beta.-unsaturated dicarboxylic acid or anhydride thereof, said parital esterification, imidation or amidation being carried out by adding to the adduct a compound having a polymerizable unsaturated group with the vinyl group.
As the result of further extensive studies of the present inventors, it has been found that the desired graft polymer emulsion having excellent properties can also be produced by using a wide range of oligomers having an unsaturated group other than the polybutadiene etc., having 1,4-bonds as the base polymer.
For instance, when a 1,2-bond polybutadiene having a pendant vinyl group, which is graft polymerizable, is partially esterified by introducing 2-hydroxyethyl methacrylate and then is graft-polymerized, an emulsion having excellent performance, such as excellent coating film properties and stability, can be produced. It is assumed from this fact that the graft polymerizability owing to the methacryl or acryl group introduced by the present invention contributes far more to the improvement of the performances of emulsion than does the graft polymerizability owing to the pendant vinyl group of the liquid 1,2-vinyl polybutadiene.
Moreover, it has been found that the desired graft polymer emulsion having excellent performance properties can also be produced from unsaturated polymers such as petroleum resins, natural drying or semidrying oils or unsaturated fatty acids which compose the natural drying or semidrying oils of the present invention.
Another embodiment of the present invention provides a process for emulsion-polymerizing oligomers, which are produced by introducing a polymerizable unsaturated group (e.g. acryl or methacryl group) into the above unsaturated polymers, in an aqueous medium.
It is well known that the drying characteristics and coating film properties of paints can effectively be improved by enlarging the molecular weight of the vehicle resin. However, this produces various defects, such as too high viscosity, or difficult handling during the preparation thereof and the painting. These defects, particularly the high viscosity, can be eliminated by the emulsion polymerization of the present invention.
The polymer emulsion can be formed by the crosslinking polymerization of synthetic oligomers or natural drying or semidrying oils, which have unsaturated groups having a high oxidative polymerizability in the main chain, in fine emulsion particles.
The polymer emulsion of the present invention consists of fine particles and a low viscosity while the polymer per se has a high molecular weight and is occasionally crosslinkaged, and the polymer emulsion can give a coating film having excellent gloss and toughness.
An object of the present invention is to provide a novel polymer emulsion having excellent performance properties, particularly excellent coating film properties.
Another object of the present invention is to provide a vinyl graft polymer emulsion or high molecular weight polymer emulsion useful for paints, adhesives, fibers, papers, or the like.
These and other objects and advantages of the present invention will be apparent from the following detailed description given hereinafter; it should be understood, however, that the detailed description and accompanying specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. These changes and modifications are intended to be ecompassed within the scope of this invention.